Field
The embodiments described below relate generally to the delivery of therapeutic radiation to a patient. More specifically, some embodiments are directed to the generation of radiation treatment plans.
Description
According to conventional radiation treatment, a beam of radiation is directed toward a target volume (e.g., a cancerous tumor) located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the target volume according to an established treatment plan. The delivered radiation kills cells of the target volume by causing ionizations within the cells or other radiation-induced cell damage.
Treatment plans are designed to deliver a particular radiation dose to a target volume, while ensuring that surrounding healthy tissue does not receive an unsafe dose. Treatment plan design therefore requires the identification of various tissues within a patient volume (i.e., to identify targets, surrounding tissue and organs-at-risk), and the electron densities of the various tissues (i.e., to calculate the dose delivered to those tissues).
Computed tomography (CT) imaging may be employed to acquire an image of a patient volume for treatment planning purposes. CT images may provide a level of clarity suitable for tumor and organ delineation. Moreover, CT images provide a good representation of the electron densities of imaged tissues. Magnetic resonance (MR) imaging typically provides clearer differentiation of tissue types in comparison to CT imaging, and is therefore particularly suitable for tumor and organ delineation. However, MR images do not adequately represent the electron density of the imaged tissues.
Some conventional systems include acquisition of a CT image and an MR image of a patient volume, and combination of the CT image and the MR image. A treatment plan may then be designed based on the combined image, with the initial delineation step being performed based on the MR data and the dose calculation step being performed based on the CT data. A positron emission tomography (PET) image may also be acquired and combined with the CT image and the MR image in order to assist in identifying malignancies.
Facilities using the foregoing systems require an MR scanner and a CT scanner, in addition to a linear accelerator (LINAC) which will be used to execute the designed treatment plan. Due to the attendant costs, it has been proposed to design treatment plans based solely on MR images. According to this proposal, an MR image is used to delineate tissues, and each tissue type is assigned an electron density based on predefined values. The assigned electron densities are then used for the dose calculations described above. However, the electron densities for particular types of tissues will vary from patient to patient, so doses calculated in this manner for a given patient will be less accurate than doses calculated using electron densities which are determined from a CT image of the patient.
Systems are needed to facilitate treatment planning while addressing one or more shortcomings of existing systems.